Lubricating compositions



Unite LUBRICATING COMPOSITIONS No Drawing. Application January 24, 1955Serial No. 483,824

Claims priority, application Great Britain January 26, 1954 Claims. (Cl.252-466) The present invention comprises improvements in or relating tolubricating compositions and relates particularly to fluid lubricantscapable of use over a very wide range of temperatures.

It is an object of the present invention to provide lubricatingcompositions suitable for use over a wide range of temperatures andunder a variety of conditions and suitable for use in internalcombustion engines or other mechanisms where high temperatures areinvolved e. g. in the lubrication of gas turbines, especially thepropeller turbine type where the lubricant is required to lubricate notonly thebearings but also the reduction gearing, said lubricatingcompositions also being stable and fluid at low or very low temperaturese. g. down to 40 F. or even 80 F.

It. has already been proposed to employ as lubricants (especially suitedfor use at low temperatures) certain diesters of aliphatic dicarboxylicacids with branchedchain aliphatic alcohols, a number of such estersbeing described in the Journal entitled Industrial and EngineeringChemistry, April 1947, p. 484 to p. 497.

These esters possess extremely low pour-points, have excellentviscosity-temperature characteristics and good lubricating propertiesand have been found very satisfactory lubricants for a variety ofinstruments such as watches, clocks, aeronautical compasses, gyroscopes,meters, gun-turret mechanisms and a variety of aircraft and otherscientific instruments, especially where, as in aircraft, very lowtemperatures are encountered.

It has also been proposed to stabilise such esters by the addition ofantioxidants such as organic amines and phenols of various types.

In our British patent specification No. 696,064 it has been proposed tostabilize these esters by the addition of minor amounts of metal saltsof organic dithiophosphoric acids, with or without the further additionof metal salts of oil-soluble petroleum sulphonic acids. By this meansthe esters could be stabilized against oxidation at relatively hightemperatures, and rendered suitable for the lubrication of internalcombustion engines and gas turbines.

Recent improvements in the design of gas turbine engines have increasedthe severity of the demands made upon the lubricant, which must havegood oxidation resistance at high temperatures, 6. g. of the order of200 C., at. the same time being non-corrosive towards metals used in theconstruction of the turbine engines, e. g. steel, copper, brass,magnesium, aluminium and cadmium-plated steel. It must also possess ahigh load-carrying capacity, in order to provide adequate lubrication ofthe reduction gearing in the propeller-turbine type of engines.

In our United States application Serial No. 456,063 we have disclosedthe fact that dicarboxylic acid diesters may be very efl ectivelyinhibited against oxidation at high temperatures by the addition ofminor amounts of hydroxy-substituted diaryl thioethers, and that a stillfurther improvement may be obtained by the inclusion of a basic ice 2aliphatic, alicyclic or heterocyclic amine having a boiling point of atleast C.

it has previously been proposed to increase the loadcarrying capacity ofdicarboxylic acid diesters by the incorporation therein of tritolylphosphate, formerly known as tricresyl phosphate, but in general ithasbeen considered necessary to use a relatively large amount, e. g.of'the order or 5%, to produce adequate lubrication of the reductiongearing of propeller type gas turbines.

We have now found that by the addition to dicarboxylic acid diesters, ofthe type described in United States patent application Serial No.456,063 of both (a) a hydroxysubstituted diaryl thioether, and (b) aneutral organic phosphate or phosphite ester, the load-carrying capacityof these esters can be very substantially enhanced.

The degree of improvement obtained is considerably in excess of that tobe expected from consideration of the extreme pressure properties of thetwo types of additives when used singly. Thus, the hydroxy-substituteddiaryl thioethers of the present invention have little or no efiect onthe load-carrying capacity of the esters while, as has already beenstated, fairly large quantities of neutral organic phosphate esters arerequired to produce adequate lubricating properties. under extremepressure conditions. By the conjoint use of the two types of additives,however, lubricants can be obtained having adequate extreme pressureproperties and excellent resistance to oxidation at high temperatures,Furthermore, the total amount of combined additives required to impart aparticular degree of load-carrying ability is substantially less thanthe amount of organic phosphate ester which would be required, if usedalone, to give the same result,

According to the present invention there is provided a lubricatingcomposition as claimed in any one of the claims of United States patentapplication Serial No. 456,063 which lubricating composition hasincorporated therein a minor proportion of a neutral organic phosphateor phosphite ester.

The term neutral ester used throughout the specification and claims isto be understood as referring to esters having an acidity not exceeding1 mg. KOH per gm.

The preferred esters have the general formula COOR: B

\COOR2 where R is an aliphatic or cycloaliphatic hydrocarbon radicalhaving from 2 to 8 carbon atoms, and R and R; are the same or differentand are branched-chain alkyl or alkyl-substituted cycloalkyl radicalshaving at least 4 carbon atoms. Examples of the radical R are -CH=CH (CH(where n is an integer from 2 to 8)- and CH2 Cfi CH.CHi-

c a CHs While esters having the above general formula are preferred, itis also within the scope of the invention to employ esters obtained byesterifying. the dicarboxylic acids with a mixture of an alcohol and aglycol to give complex esters having, the general formula R OOC.R.COOROOC.R-COOR wherein R, R and R are as defined above and OHf is a glycolor polyglycol having not more than about 12 carbon atoms.

Other types of complex esters which may be employed are prepared byesterifying a dicarboxylic acid (1 mol) with a glycol (2- mols) and amonocarboxylic acid (2 mols) or with 1 mol each of a glycol, amonocarboxylic acid and a monohydric alcohol.

Esters may be employed derived from succinic, maleic, pyrotartaric.glutaric, adipic, pimelic, suberic, azelaic, sebacic and pinic acids,specific esters being:

Di l-methyl-4-ethyl octyl) glutarate Di (2-ethyl hexyl) adipate Di(3-methyl butyl) azelate Di 2-ethyl hexyl) azelate Di (2-ethyl hexyl)sebacate Di (3 5 S-trimethylhexyl) sebacate Di (2-ethyl hexyl) maleateDi (methyl cyclohexyl) adipate 2 ethyl hexyl l-methyl heptyl sebacate Di(Z-ethyl hexyl) pinate Whereas the majority of esters falling within theforegoing class possess both a high viscosity index and low pour-point,certain of them e. g. di (1:3 dimethyl butyl) adipate, di (Ii-methylbutyl) sebacate have relatively high .freezing points (above 0 F.), andtherefore would not normally be suitable for the purposes of thisinvention, except .in admixture with other esters of lower freezingpoint.

It will be understood that different esters may be selected according tothe conditions under'which the lubricant is to be used. Thus for use atvery high temperatures it will be preferred to employ the esters of highmolecular weight and particularly the higher branched-chain di-esters ofazelaic and sebacic acid.

The complex esters which may be employed are preferably prepared byesterifying 2 mols. of the dicarboxylic acid, 2 mols. of thebranched-chain aliphatic or alkyl- -substituted cycloaliphatic alcohol,and not more than 1 mol. of glycol. Examples of glycols which maybe usedare ethylene, propylene and hexylene glycols and the polyglycols, e. g.diethylene, triethylene, and tetraethylene glycol.

When a monocarboxylic acid is used in preparing a complex ester thisshould be a straight or branched-chain aliphatic acid having from 2-10carbon atoms inclusive.

Specific examples of suitable complex esters which may be employed inaccordance with the present invention are:

Ester prepared from ethylene glycol (1 mol), sebacic acid (2 mols) and2-ethyl hexanol (2 mols).

Ester prepared from triethylene glycol (1 mol) adipic acid (1 mol),n-caproic acid (1 mol) and 2-ethyl hexanol 1 mol).

The hydroxy-substituted diaryl thioethers to be employed in accordancewith the present invention have the general formula wherein the radicalsAr are aromatic nuclei which may Di(3-methoxy-4-hydroxyphenyl)thioetherbe the same or different, but are' preferably the same,

from 0.1 percent to 2.0 percent, by weight on the weight of the finalcomposition.

Specific examples of hydroxy-substituted diaryl thioethers are:

pp'-Dihydroxy diphenyl thioether Di 3-m ethyl-4-hydroxyphenyl) thioetherDi(4-methyl-3-tertiary butyl-Z-hydroxyphenyl) thioether Thioetherprepared from tertiary butyl catechol Thioether prepared from o-phenylphenol These compounds can be prepared by well known methods such as bythe action of sulphur dichloride on the desired phenol in an inertsolvent such as benzene or carbon tetrachloride or, in the case of thelast compound, by the action of sulphur dichloride on o-phenyl phenol inthe presence of a metal catalyst such as copper powder or ironfilings.Their use in mineral lubricating oils has been known for someconsiderable time, but although possessing antioxidant properties tosome degree they have not found wide application in internal combustionengine oils and have been considered inferior to the metaldithiophosphates and other metal-containing additives. It is importantthat compounds for use in conjunction with the diesters of, the presentinvention should be substantially free from the corresponding diandpolysulphides and from free sulphur.

In view of the fact that these thioethers have had such limitedusefulness as antioxidants in mineral oils, it is not a littlesurprising to'find them so effective as antioxidants in diester typelubricants. Moreover, whereas thioethers derived from alkylated phenols,e. g. tertiary butyl phenols and cresols (which themselves haveantioxidant properties) have apparently always been preferred for use asantioxidants for mineral oils, we have found that for the. purposes ofthe present invention the best results are obtained by the use ofthioethers derived from phenols which are unsubstituted or substitutedonly by short alkyl radicals such as methyl groups and preferably by notmore than one methyl group, although the use of more highly alkylatedphenols is not excluded. This preferred class of phenol thioethers havegood solubility in the esters of the present invention, but theirsolubility in most mineral oils is so limited that their use asantioxidants in that connectionwould hardly be considered.

In addition to the simple thioethers, examples of which have beenquoted, it is possible to use polymeric compounds such as those obtainedby the action of more than one (but less than 2) mols. of sulphurdichloride, on 2 mols. of a phenolhaving at least two free orthoorparapositions in the nucleus.

It will be understood that the compounds selected for use must haveadequate solubility in the esters in which they are to be dissolved.Thioethers in which the radicals Ar in the above general formula consistof condensed arylnuclei, e. g. naphthyl groups, have inadequatesolubility unless compensating nuclear alkyl substituents or ethergroups are present. Similarly, compounds in which x y or z are more thanI tend to lack solubility and must be compensatedin the same way.Generally it is preferred to employ compounds in which the radicals Arare phenyl radicals and x and z are 1 n being zero.

The neutral organic phosphate esters of the present invention have thegeneral formula Ra0 where R R and R are organic radicals and mayrepresent alkyl, aryl, alkaryl or cycloalkyl radicals. Preferably R Rand R will be the same, but if desired mixed esters of phosphoric acidmay be employed. It is also within the scope of the invention to employesters containing more than one phosphate grouping in the molecule, e.g. di-phosphates having the general formula where R, and R are asdefined above and R is an alkylene or arylene radical.

"methyl'phosphate, boiling at 197 C.

Trimethyl phosphate Triethyl phosphate "Tri (n-butyl phosphateTri(2-ethyl hexyl) phosphate Triphenyl phosphate Tri-o-tolyl phosphateTri-m-tolyl phosphate Tri(p-tertiary amyl phenyl) phosphate Tri (methylcyclohexyl) phosphate Tri (butoxyethyl) phosphate Tetraethyl p-phenylenediphosphate It will be understood that the particular phosphate estersselected .must possess adequate solubility in the dicarboxylic aciddiesters in which they are to be used. Consequently, it is preferred ingeneral to employ phosphate esters in which at least one of the radicalsR R or R contains at least two carbon atoms, or, if the radicals arearyl radicals, that-at least one of them, and preferably all three,contains an alkyl substituent.

The neutral organic phosphite esters of the present invention contain atleast one atom of trivalent phosphorus attached through oxygen tohydrocarbon radicals, and may have the general formula:

R20 where R R and R are organic radicals and may represent alkyl, aryl,alkaryl or cycloalkyl radicals. Preferably R R and R will be the same,but if desired mixed esters of phosphorous acid may be employed. It isalso within the scope of the invention to employ esters containing morethan one phosphite grouping in the molecule.

Since the lubricants are required for use at high temperatures, it isnecessary that the phosphate and phosphite esters employed should haveboiling points not below about 200 C. and that, when dissolved in thesynthetic ester lubricant of the present invention, in the proportionsin which they are to be employed, they should not sufier decompositionat this temperature. The neutral organic phosphate esters are thermallystable substances of high boiling-point, even the lowest member of theseries, tri- In employing the "phosphite esters, however, it ispreferred to select compounds in which the sum of the carbon atomscontained in the radicals R R and R is not less than 12.

Any or all of the hydrocarbon radicals of the phosphate or phosphiteesters may carry hydrocarbon, ether or ester substituents, provided thatthese do not impair the stability of the compound at elevatedtemperatures. The presence of other substituents, however, e. g. halogen'iand'sulphur-bearing groups, other than thioether groups linking twoaromatic nuclei, will in general be inadmissible on this account.

One particular class of sulphur-bearing phosphite esters which We havefound suitable for the present invention is the phosphite esters ofaromatic hydroxy-substituted thioethers, some examples of which, alongwith other closely related compounds, are described in our United StatesPatent No. 2,396,839.

Those suitable for use in the present invention have the generalformulae:

where the radicals R are hydrocarbon radicals which may carry ether orester substituents, the radicals Ar are aromatic radicals which maycarry alkyl,-ether or ester substituents, m is zero, 1 or 2, and n is asmall integer from H0 3, the sum ofm and n being 3.

Specific examples of phosphite esters which may be employed in'thepresent invention are:

Tri(n-butyl) phosphite Triphenyl phosphite Tritolyl phosphiteTricyclohexyl phosphite V Di( 3 carbomethoxy 4 hydroxyphenyDthioetherditolyl phosphite.

The phosphite esters possess themselves more effective load-carryingproperties than the corresponding phosphate esters, and can therefore beused in lesser amounts. The joint use of these phosphite esters with thearomatic hydroxy-substituted thioethers, however, produces a stillfurther improvement in load-carrying ability, and therefore permits afurther reduction in the amountof phosphite ester required.

In carrying out the present invention it will be necessary toincorporate the two additives in amounts sulficient to effect asubstantial increase in load-carrying capacity over that exhibited bythe dicarboxylic acid diesters alone. Thus the thioethers may beemployed in concentrations ranging from 0.2 percent to 5.0 percent, andpreferably from 0.5 percent to 2.0 percent, by weight on the weight ofthe final composition, the phosphate esters in amounts of from 0.5percent to 10 percent but preferably from 1.0 percent to 5.0 percent byWeight on the weight of the final composition, and the phosphite estersin amounts of from 0.1 percent to 5 percent but preferably from 0.25percent to 2.0 percent by weight on the weight of the final composition.

While either the simple diesters of dicarboxylic acids or the complexesters may be employed in accordance with the present invention, thesematerials have certain limitations. Thus the simple esters have rathertoo low viscosities to be suitable as such for lubricating the existingtypes of aircraft gas turbines which normally require a lubricant havinga minimum viscosity of 7.5 centistokes at 210 F., whereas the complexesters in general have insufiiciently low pour-points which shoulddesirably be of the order of 70 F. or below.

Accordingly, in a preferred form of the present invention thedicarboxylic acid diesters of the type described are thickened to thedesired degree by the addition of polymers of esters of acrylic oralkyl-substituted acrylic acids, e. g. methacrylic acid. Compositions ofthis type can be produced having sufficiently high viscosities combinedwith very low pour-points.

The polymers are employed in proportions of from 1 percent to 15percent, preferably from 3 percent to 10 percent, by weight on theweight of the final compositron.

Examples of polymers which may be employed are the polymerised n-hexyl,3:5 :5 trimethyl hexyl and lauryl esters of methacrylic acid, andvarious commercially available materials sold under the trade nameacryloid. it is preferred to use polymers which are not only freelysoluble in the diester lubricants but also miscible with mineral oil.

There may also be included in the composition an aliphatic alicyclic orheterocyclic amine having a boiling point of at least C., as disclosedin our United States patent application Serial No. 456,063. Examples ofsuitable amines which may be used are n-octylamine and higher primaryaliphatic amines, dibutylamine, and higher secondary aliphatic amines,cycloaliphatic amines such as dicyclohexylamine, and heterocyclic aminessuch as the lupetidines and higher homologues of piperidine.Tertiaryamines having basic properties may also be employed, e. g.di-n-octylmethylamine and 2:6 lutidine.

Generally these amines will be employed in relatively small amounts, e.g. from 0.01 to 1.0 percent by Weight on the weight of the finalcomposition, and preferably from 0.05 to 0.5 percent by weight on theweight of the final composition.

Other additives may be included if dcsirctLe. g. rust inhibitors such asavery small amounts "of metalpetroleum sulphonates, or other knowncompounds capable of inhibiting rust formation in presence of water.

It is also within the scope of the invention to include lubricants inwhich a certain amount of mineral oil is added .to the .composition.

lacquer and deposit-forming tendencies, and from sensitivity to light.Specific compositions which maybe employedin accordance with the presentinvention are exemplified in the tables of test results which follow. Todetermine the load-carrying capacity of the compositions of thisinvention, tests were carried out using the well-known Four-BallMachine, similar to thatdescribed by Boerlage in Engineering, July 13,1933, volume 136, page 46. This apparatus comprised four steel ballsarranged in the form of a pyramid. The top ball was held in a chuckattached to a spindle rotating at approximately 1500 R. P. M. andpressed against the three bottom balls clamped ina stationary 'baliholder. The balls were immersed in the oil to be tested. I Tests wererun for one minute at ambient temperature at a series of diiferentloads.

The ensuing tables illustrate the efiectiveness of the compositions ofthe present invention.

even at, very high temperatures, and are free from TABLE I Additivespresent Mean wear Test Initial (mms.) at; No. seizure load, kg.Thicether Phosphate or phosphite ester 100 kg. 120 kg.

1 B'n"i;"'art"'rtai"imam" 3 252% 3'? 2 6 2 p en ue er o q hgme y W p yTri -0rn tolyl phosphate 80-85 2.5 2.9 4 fln 'iri m 1 tolyl phosphate75-80 as w 5 pp'-Dihydroxydiphenyl thioether (1.0%) T123 0m -tolylphosphate 105-110 0.43 2.5 None Triphenylphosphite (1.0%)- 85-90 2.3 2.8pp-Dihydr0xydiphenyl thioether 0 90-95 2.4 2.5 pp'-Dihydroxydiphenylthioether (05%)-. Tnphcnyl phosphite (0.5%)- 90-95 2. 0 2. 4

Y W indicates that welding took place at The surprising efiectiveness(tests 2,

[In this hexyl) sebaeate, 47% Di (3:525 trirnetnyl this load.

of the combined additives (tests 5, 7,

3, 4, 6) can readily be seen from the foregoing results.

TABLE II series oi tests the additives were dissolved in a blend havingthe following composition: 47% Di(2-ethyl leum sulphonate, 0.1%dicyclohexylamine] 8) as compared with additives used singly hexyl)sebacate, 6% Polynonyl methacrylate, +0.05% calcium petro- Additivespresent Mean wear Test Initial (mms.) at- No. seizure load, kg ThioetherPhosphate ester 100 kg. 140 kg.

9------ Di(o-cresol) thioether (1.0%) None Below 2.1 W 10 Di(o-cresol)thioether (0.5%). Tri-m-toiylphosphate(3.0%). -70 2.2 g 2.8 11 ...doTri-m-tolyl phosphate(5.0%) 95-100 2.2 2. 6 12.- Di(o-creso1) thioether(0.75%) Tri-m-tolylphosphate(2.0%) -80 2.2 2.5 13 oTri-m-toiylphosphate(3.0%) 95-100 2.3 2. 55 14 Di(o-cresol) thioether(1.0%) Tri-m-tolyl phosphate(2.0%) -90 2.2 2.6 is (in Tri-m-tolylphosphate(3.0%). -100 2.2 2.5

The di(o-cresol) thioether was a commercially available materialconsisting mainly of di(3-methyl-4-hydroryphenyl) thioether.

The polynonyl methacrylate we of the polymer when dissolved in a of7.5-8.5 centistokes at e II illustrate the eflect of varying theproportions of two typical additives of thepresent s being achieved bythe use of 0.75% of the thioether with 3.0% of the phosphate ester.

The results in Tabl invention, optimum result s 3:515 trimethyl hexylmethacrylate polymerised 50/50 blend of the two sebacate esters produceda lab TABLE In [In this series of tests, the additives were dissolved ina blend having the following composition: 44% Di(2-ethyl hexyl)sebacate, 50% Di(3:5:5 trimethyl hexyl) sebacate, 6% Polynonylmethacrylate.]

to a degree such that 6% ricant having a viscosity Additives presentMean wear Test Initial (mms.) at--- No. seizure load, kg.

Thioether Phosphate or phosphite ester kg. kg.

16. Polymeric thioether prepared from p-octyl None 60-65 2. 2 2. 6

phenol (1.0%). 17- one. Tributyl phosphate (2.0%) 85-95 2. 7 3. 5 18Polymeric thioether prepared from p-octyl .do 95-100 2. 1 2. 4

phenol (1.0%). 19. None Tri(2-ethyl hexyl) phos- 70-75 2. 45

phate (3.0%). 20..-" p p-Dihydroxydiphenyl thioether (1.0%) do 90-95 2.2 2. 6 21 None Tn (methyl cyclohexyi) 65-70 2. 1 W phosphite (0.25%). i22- pp Dlhydroxydiphenyi thioether (1 .0%) m -do 85-00 2. 25 2. 5

" 1 I K i The results in Table III furtheriilustrate the advantage ofusing a combination of the two types of additives. The polymeric thiocther employed in tests 16 and 18 was prepared from 1.2 mole oi p-octyl(m2, w-tetramethyl butyl) phenol andlmol. oi sulphur dichloride inbenzene solution.

[This series of tests wasdeslgned to provide further examples of typicalcolrn T BLE V in carrying out the present inventlon.

positions which may be employed Test No.

Base blend Additives present Initial seizure Mean wear,

(mms) load, kg.

44% DOB, 50% DNS, 6% PNM..-

45% DOA, 45% DNA, 10% Acrylold H. F. 860.

40% Di(2-ethyl hexyl) maleate,

40% Di C adipate, 20% Acryloid 710 71% DOA ,17% on A, 3.3% 011B, 12.12%Polylauryl" methacry- 1.0% pp-Dihydroxydiphenyl thio- 2% Trlbutoxyethylphosphate, 2% Thioether prepared from guaiacol.

1% Trlethyl phosphate, 1.5% Thloether prepared from t-butyl catechol,0.1% Dl-n-octyl methylamine, 0.1% Calcium petroleum nprepared from mixedbranched-chain alcoholshaving'7-9 .:carbon.atoms.

--with 0.5 mol. sulphur dichloride and then treating 3- sulphonate.

'In' Table IV the abbreviations have the following significance:

DOS=di(.2-ethyl hexyl) sebacate DNS=di(3:5 :5 trimethyl hexyl) sebacatePNM=polynonyl methacrylate DOA=di(2-ethyl hexyl) adipate DNA=di(3:5 :5trimethyl hexyl) adipate 'Di C adipate was amixture of .diesters ofadipicacid Acryloid HF 860 and 710 were concentrates of polymethacrylateesters in gas oil and mineral oil, respectively, while the polylaurylmethacrylate was a comparatively low molecular weight co-polymerprepared from the mixed methacrylate esters of commercial lauryl alcohol(83%) and 3:5:5 trimethyl hexanol (17%).

p-Octyl phenol thioether phosphite was prepared by treating l-mol. ofp-octyl (uw 'y-tetramethyl butyl) phenol mole of the resulting thioetherwith l-mol. of phosphorus trichloride in presence of.3-mo1s of pyridinein benzene solution.

Oil A. was a solvent refined mineral oil of viscosity below.

It will readily be seen that these compositions have excellentviscosity-temperature characteristics and very low pour points, inaddition to good load-carrying properties.

To determine the oxidation stability of the compositions of thisinvention at elevated temperatures, a modification of the well-knownBritish Air Ministry oxidation test was employed. "This test wascarriedout precisely as described'in Standard MethodsforTesting'Petroleum and its Products, InstituteofPetroleum,1949,'Method I. P. 48/44, with the exception that there waspresent a copper catalyst consisting of apiece of polished copper foil2' inches X 1% inches rolled into a cylinder as'described in I. P.Method 56/46, this being replaced by a fresh catalyst after every 3hours. Additionally there were present strips of polished copper foil 6inches x /2 inch suspended in the-vapour phase above the oil, the lowerportion of. the strips beingiolded into three Segments approximately 1inch long, so'that the overall length of the strip above the oil wasabout 3 inches and the lower end of the strip was'3 /z inches above thesurface of the oil.

After air blowing, the percentage increase in viscosity and acidity risewere determined together with the'percentage of matter insoluble inpetroleum ether (boiling point below 40 C.). Also the vapour-phasecopper strips were examined for signs of attack by volatile acids, asevidenced by the presence of a green colour.

about 150 seconds Redwood at 140 F., and Oil B. a 60 TABLE Vsolvent-refined mineral oil of viscosity about seconds Redwood-at isPomp... see It is to .be understood that the foregoing examples o e o o)a a, de n o t "merely-afiord illustrations of typical compositions.of.the 210 O :present invention, and that any of the esters orthioethers 65 1 o exemplifiedin our United States applicatiouSerial N0.g; 338 456,063. may be employed as alternatives. 28-07 The physical:properties of certain typical compositions in the preferred viscosityrange are quoted in Table V pp Table VI illustrates the vetiectivenessof the compositions of the present invention as compared withcompositions containing only the phosphate or phosphite esters. Thetemperature of the tests was 200 C. and the duration 12 hours.

TABLE VI Percent Attack of insoluble vapour Percent Acidity inpetrophase Test Ester or ester blend Additives viscosity (mgs. leurncopper No. change KOH ether strips,

per gram) (B. B. observed below after- 40" O.) V

28..." 44% i o os, 50% DNS, 6% N 7 10.0 4.5 Trace 3hrs. 29 an 2.0%tri-m-tolyl phosphate, 0.05% calcium +7.5 3.5 3.0 Bhrs.

petroleum sulphonate. 30 do 0.5% lIlzriphenyl phosphite. 0.1%dicyclohexyla- +23. 8 17.4 0.33 6 hrs.

in e. 11 do- 0.5% triphenyl phosphite, 0.1% dicyclohexyla- +1. 6 1.7 0.14 6 hrs.

mine, 1.0% polymeric thioether" prepared from p-octyl phenol, 0.05%calcium petroleum sulphonate. 32..-.- 47% DOS, 47% DNS, 6% 2.0%tri-m-tolyl phosphate, 0.05% calcium +8.0 1.7 0.77 Absent.

ZPNM. petroleum sulphonate, 1.0% pp-dihydroxy I diphenyl thioether. I33-.-.- 44% DOS, 48.8% DNS, 7.2% 0.5% di(o-cresol) thioether, 1.0%di(3-carbo- +2.7 2.2 Do.

PNM. methoxy-t-hydroxyphenyl) thioether ditolyl phosphite, 0.05% calciumpetroleum sulphonate, 0.1% dieyciohexylemine.

It has been found that when an organic phosphite ester is employed inconjunction with a hydroxy-substituted diaryl thioether, particularlygood resistance to oxidation 7 is obtained, and such blends are evenless prone to stain metals such as copper at high temperatures than thecorresponding blends containing phosphate esters or containing only thethioethers. Some further degree of improvement in oxidation andcorrosion resistance is obtained by the inclusion of a basic aliphatic,alicyclic or heterocyclic amine having a boiling point of at least 140C.

It is accordingly particularly preferred to employ compositionscontaining a hydroxy-substituted diaryl thioether, an organic phosphiteester as hereinbefore defined,

andvan amine of the type described, such compositions being superiorwith respect to load-carrying capacity and radicals selected from thegroup consisting of branchedchain alkyl and alkyl-substituted cycloalkylradicals having at least four carbon atoms, from 0.2% to 5.0% of ahydroxy-substituted diaryl thioether having the general formula R. 7 sR.

where R is a memberof the group consisting of H and a CH radical and nis an integer not exceeding 4, and

from 0.25% to 5.0% of, a neutral organic ester selected from the grouphaving the general formulas Rrb\ ' Rio-P and where R R and R areradicals selected from the group consisting of alkyl, aryl, alkaryl andcycloalkyl radicals.

2. A lubricating composition comprisingia maior proportion of at leastone ester of the general formula COOR:

where R is a radical selected from the group consisting of aliphatic andcycloaliphatic hydrocarbon radicals having from two to eight carbonatoms, and R and R, are radicals selected from the group consisting ofbranched-chain alkyl and alkyl-substituted cycloalkyl radicals having atleast four carbon atoms from 0.2% to 5.0% of a hydroxysubstituted diarylthioether having 'the general formula OH HO where Ris a member of thegroup consisting ofH and a CH radical and n is an integer not-exceeding4, and from 1.0% to 5.0% of a neutral organic phosphate ester, havingthe general formula where R ,-R and R are radicals selected fromthegroup consisting of alkyl, aryl, alkaryl and cycloalkyl radicals.

3. A lubricating composition comprising a majonproportion of at leastoneester of the generalformula ooon1 B\ r g 0003:

on no where R is a member of the group consistingof H and a 15CI-hradical and n is an integer not exceeding 4, and from 0.25% to 2.0%of a neutral organic phosphite ester having the general formula RsOWhere R R and R are radicals selected from the group consisting ofalkyl, aryl, alkaryl and cycloalkyl radicals.

4. A lubricating composition comprising a major pro portion of at leastone ester selected from the group consisting of di(2-ethyl hexyl)azelate, di(2-ethyl hexyl) sebacate, di(3:5:5-trimcthylhexyl) azelateand di(3:5:5- trimethylhexy) sebacate, from 0.25 to 2.0% of a neutralorganic phosphite ester selected from the group consisting of triphenylphosphite, tritolyl phosphite and di(3-carbomethoxy-4-hydroxy phenyl)thioether ditolyl phosphite, and from 0.2% to 5% of a hydroxysubstituted diaryl thioether selected from the group consisting of ppdihydroxy diphenyl thioether and di(o-cresol) thioether, said thioetherbeing present in suflicient quantity further to increase theload-carrying capacity of the composition.

5. A lubricating composition comprising a major proportion of at leastone ester selected from the group consisting of di(2-ethyl hexyl)azelate, di(2-ethyl hexyl) sebacate, di(3:5:5-trimethylhexyl) azelateand di(3:5:5- trimethylhexyl) sebacate; from 1.0% to 5.0% of a neutralReferences Cited in the file of this patent UNITED STATES PATENTS2,139,766 Mikeska et al Dec. 13, 1938 2,396,839 Evans Mar. 19, 19462,499,984 Beavers et a1. Mar. 7, 1950 2,639,266 Dilworth et al May 19,1953 2,760,934 Black Aug. 28, 1956 FOREIGN PATENTS 455,235 Great BritainOct. 15, 1936 OTHER REFERENCES Ind. and Eng. Chem., vol. 39, No. 4 pages491-497, pages 492 and 493 pertinent.

Lubrication Engineering, August 1952, pages 177, 178, 179, 197, 198, 199and 200, page 178 pertinent.

1. A LUBRICATING COMPOSITION COMPRISING A MAJOR PROPORTION OF AT LEASTONE ESTER OF THE GENERAL FORMULA